1. Field of the Invention
The present invention relates to a liquid transport apparatus which transports a liquid, and a method for producing the liquid transport apparatus.
2. Description of the Related Art
A liquid transport apparatus (piezoelectric pump) has been hitherto known, which transports a liquid by applying the pressure to the liquid by utilizing the deformation of a piezoelectric element brought about when a voltage (electric field) is applied. For example, a piezoelectric pump, which is described in Japanese Patent Application Laid-open No. 6-147104, is provided with two pump chambers which have same shape (circular shape) and which are communicated with each other, a pressure-adjusting chamber which is communicated with the pump chamber disposed on the downstream side and which has the same shape as that of the pump chamber, and piezoelectric elements which are arranged to cover the two pump chambers from upper and lower portions respectively. A voltage is applied to the piezoelectric element corresponding to each of the pump chambers to cause the deformation so that the volume of the pump chamber is changed. Accordingly, the pressure is applied to the liquid contained in the pump chamber, and thus the liquid is transported. Thin films are arranged at upper and lower positions with respect to the pressure-adjusting chamber. The pressure of the liquid fed from the pump chamber is adjusted in the pressure-adjusting chamber by means of the elastic deformation of the thin films.
A piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077 (FIG. 2) is provided with a pump chamber, a liquid supply passage and a liquid discharge passage which are communicated with the pump chamber, and three piezoelectric transducers or oscillators (first, second, and third piezoelectric transducers) which are provided corresponding to the pump chamber, the liquid supply passage, and the liquid discharge passage respectively. The first piezoelectric transducer, which corresponds to the pump chamber, is arranged to cover the pump chamber. The volume of the pump chamber is changed in accordance with the deformation thereof to apply the pressure to the liquid in the pump chamber. On the other hand, the second and third piezoelectric transducers are provided at intermediate portions of the liquid supply passage and the liquid discharge passage respectively. The liquid supply passage and the liquid discharge passage are opened and closed in accordance with their own deformation. In this case, the liquid supply passage and the liquid discharge passage extend from the side wall of the pump chamber in the horizontal direction perpendicular to the side wall. Therefore, the piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077 has such a three-dimensional structure that the first piezoelectric transducer which is provided to apply the pressure to the liquid in the pump chamber and the second and third piezoelectric transducers which open and close the liquid supply passage and the liquid discharge passage respectively are positioned on mutually different planes.
The piezoelectric pump described in Japanese Patent Application Laid-open No. 6-147104 is not provided with any means for closing the flow passage disposed on the upstream side of the pump chamber when the piezoelectric element is deformed to apply the pressure to the liquid in the pump chamber. For this reason, even when the pressure is applied to the liquid in the pump chamber, a part of the pressure wave escapes toward the upstream side. Therefore, the transport efficiency is unsatisfactory. A valve mechanism for opening/closing the flow passage disposed on the upstream side of the pump chamber can be provided distinctly from the piezoelectric pump. However, the number of parts is increased, and the structure is complicated as well, which is disadvantageous in view of the production cost.
In the case of the piezoelectric pump described in Japanese Patent Application Laid-open No. 64-32077, the first piezoelectric transducer for applying the pressure to the liquid in the pump chamber and the second and third piezoelectric transducers for opening/closing the liquid supply passage and the liquid discharge passage are not arranged on the same plane. For this reason, the structure of the piezoelectric pump is complicated, and it is difficult to miniaturize the pump. Further, when the pump is produced, it is necessary that the first piezoelectric transducer and the second and third piezoelectric transducers should be arranged in separate steps. The number of steps is increased, and the production cost is increased corresponding thereto.